There is a tiny transparent spot on a CD-R, caused by disc rot.
But if I just run through it with full CAV ×48(BE14NU40)/×52(GDR-H20N)/×24(HL-DT-ST BU20) speed, it reads the data in a way as if there were no errors.
But if I read it at low speeds such as CAV speed ×16, the drive heavily fails reading that spot.
For some CDs, the readability is even better at lower speeds, eg. the CD cracked at the inner edge is as good as unreadable at any high speed. The lens loses track.
But for disc rot spots, and dusty discs, the lens rather loses track at lower speeds and reads without flaws at high speeds.
For the old GDR8162B, in DAE, high speeds cause more noise, but low speeds can cause the lens to lose track. Then, the drive makes hiccups and coughing sounds.
Why do some drives handle disc damage errors much better at increased speeds?